Many Christians who affirm the inspiration and authority of the Bible have a way, nonetheless, of practically decanonizing the OT. And that's because they don't know exactly where the moral law leaves off and the ceremonial law begins. For them, the law of Moses might as well be an electrified fence.
And, of course, if you ask the question that way, then you are condemned to moral paralysis, for only God knows precisely where the line lies at every point along the way.
But since Christian duty does not depend on our having divine omniscience, then that is surely the wrong way to pose the question. So let us approach the issue from another angle.
1. Assuming that God never does what is wrong or orders what is wrong, then how is what was right in the past wrong at present? Put another way, how far wrong can we go by continuing to do what was right in the past?
To take a couple of examples, Christians get hung up over the blue laws. Should we or should be not have blue laws today? Is this part of the moral law or the ceremonial law?
Now we could try to answer that question as stated. On the basis of Gen 2:2-3 it would be easy, I should think, to argue that this is a creation ordinance.
But I want to invoke a broader principle. If blue laws were commanded in the past (under the Mosaic law), then blue laws were right at that time. And if they were right way back when, then how can they be wrong today? How can they be morally wrong nowadays if they were not morally wrong in the days of yore?
Or, to take another example, consider the whole debate over queer rights. Now, under the OT, a sodomite did have rights: he had the right to die! Sodomy was a capital offense. So, if sodomy was a sin in the past, how can it be a right at present?
2. This brings me to another point. Even if something that was once morally mandatory in the past is no longer imperative today, it would at least be permissible today. If the greater was right, surely the lesser is right.
So even if we should say that homosexuals ought not to be executed today (and I'm not saying that they shouldn't be), yet if, under the law of God, sodomy used to carry the death penalty, then it is hard to see how we can do a complete 180 and suddenly say that homosexuals are now entitled to special rights or equal rights or civil rights or human rights. (This is even before we bring the NT witness to bear.)
One can extend this to other issues. If blasphemy and idolatry used to be capital crimes (under the Mosaic law), then even if we didn't believe that we are mandated to mete out the same sentence in our own day, yet how can the promotion of a false faith (e.g., Islam) become a civil right? If the greater was right (death for blasphemy/idolatry), surely the lesser is right, viz., expelling Muslims from the country.
Suppose that Sabbath-keeping figured in the ceremonial law. Yet how bad can it be to keep Sabbath? Is it a sin to keep Sabbath? Not even a Baptist believes that. Even if we said that Sabbath-keeping is no longer necessary, is it necessarily wrong?
But suppose that Sabbath-keeping figures in the moral law? How bad can it be not to keep Sabbath? That would be a sin.
In fact, you will notice that the Apostles continued to attend the Temple, keep Kosher, and observe circumcision—even though that was all part of the ceremonial law.
Not everything that is no longer prescribed is thereby proscribed. The ceremonial law was no longer binding on believers. But it was forbidden to believers. Rather, it was a point of liberty.
So, when in doubt, play it safe. When in doubt, be cautious and conservative rather than radical and iconoclastic.
3. And this brings me to yet another point: on issues over which the faithful may disagree, over which both sides are in some degree of doubt, over which either side could be mistaken, in what direction should we err?
Should we give the benefit of the doubt to God's past commands, or should we presume that they are null-and-void? It seems to me that even if the individual issue is not obvious, the presumption should be obvious. The onus is on continuity, in the absence of contrary evidence.
Given a measure of uncertainty regarding the present application, I'd rather bet on what God has said and done in the past than gamble on a change in God's modus operandi.
Put another way, even if I turn out to be mistaken, I can't go very far wrong with a burden of proof based on moral continuity. But it's easy to see how I could go very far wrong indeed by reversing the burden.
Of course, the question of how relevant OT ethics are to Christian ethics cannot avoid the debate over theonomy. I'll state a few of the major objections, and offer a few brief replies.
Objections to theonomy:
1. Theonomy is a prescription for big gov't.
i) Theonomy is often equated with a totalitarian big brother, big gov't, command-and-control apparatus. But theonomy is about the law, not the law enforcement mechanism, per se. Under the OT you had both a tribal oligarchy and a constitutional monarchy.
ii) The scope of gov't is directly proportional to the scope of the law. The more laws there are on the books, the greater the reach and power of gov't to enforce those laws.
Compared to our modern-day civil and criminal code, the Mosaic law is pretty minimal. So this is a recipe for limited gov't, not big gov't or big brother.
iii) But if the state is governed by man-made law rather than divine law, then that is a recipe for a totalitarian state, for the state thereby defines right and wrong. Rights are conferred or rescinded at the whim of the state.
2. Theonomy forces unbelievers to play at being believers.
Even under the OT theocracy, you didn't have the same law for everyone across the board. For example, uncircumcised resident aliens were not allowed to participate in the Passover (Exod 12:43-49).
3. Theonomy criminalizes sin.
Under the Mosaic law, not every sin is a crime. We can sin in thought, word, and deed, but the law is principally concerned with the third category, far less so with the second, and not at all with the first.
4. Theonomy is harsh, meting out the death penalty for adultery, blasphemy, sodomy, Sabbath-breaking, witchcraft, juvenile delinquency, &c.
i) We naturally flinch and squirm at some of these examples. This is owing, in some measure, to our permissive social conditioning, as well as our fellow feeling. But that has nothing to do with divine justice.
ii) And I don't see that what was once right now becomes wrong, or vice versa. It seems to me that our unease and discomfort is the same in their original context as it would be in a contemporary recontextualization.
iii) Adultery and divorce are extremely destructive to the social fabric, viz., children of broken homes.
iv) As to executing juvenile delinquents, there's quite a difference between a four-year old who refuses go to bed and a sixteen year old who assaults his father or mother. There is also a difference between an isolated incident and incorrigible delinquency.
Younger and younger kids are committing worse and worse crimes. It's a tragedy for a teenager, just entering into manhood, to throw his life away, but it's even more a tragedy for the victim's whose life he took.
v) When we talk about witchcraft we need, in some measure, to clear our minds of Salem or Bewitched or Malleus Maleficarum, and concentrate on what witchcraft consisted of in OT times. We also need to consider the toll on children raised in this environment.
vi) Organizations like NAMBLA, as well as the Catholic sex scandal, illustrate the predatory nature of sodomy. Sodomites regularly lobby for the lowering or abolishment of an age of consent.
Although the church ought to have an outreach ministry to the homosexual community, we should not be more merciful to the homosexual than we are to his actual or potential victim. The wellbeing of minors must take precedence.
In addition, to the extent that homosexuals are allowed to infiltrate the institutions of power, they will use their power to extirpate the church.
5. Theonomy is thin on due process, viz., rules of evidence, right to counsel, appellate process.
This really depends on how we define a fair trial. I define a fair trial as a trial in which the guilty are convicted and the innocent acquitted. It's not about due process, per se, but getting your due. Due process ought to be adapted to that end.
However, modern-day courts seem to define a fair trial as a trial in which a guilty defendant has a chance of getting acquitted. In addition, courts seem less concerned with guilt or innocence than they do with civil rights--as they define civil rights. If the civil rights of the defendant are violated, the court will sanction the police or the DA by tossing out probative evidence or letting the accused walk on a technicality.
Due process is a good thing when it serves the purpose of establishing guilt or innocence. I think it is a bad thing when it becomes an end in itself rather than a means to a just end.
6. Theonomy can't draw a bright line between the moral and ceremonial law.
i) Borderline cases are a problem, not only for theonomy, but ethics in general. For instance, we arm our police to defend the life and limb of the innocent; but if a policeman gets into a shootout, he may accidentally injure or kill and innocent bystander in the crossfire.
The first thing I'd say is that not all cases are borderline cases, and so the borderline cases do not invalidate the non-borderline cases.
ii) Where there's a gray area, I'd give the benefit of the doubt to leniency rather than severity.
iii) Ultimately, it would be up to the political process to draw the lines.